- SLE is characterized by excessive activation of both B and T lymphocytes. Recent therapeutic approaches have involved the use of anti-CD40 ligand and CTLA4Ig, agents that antagonize the costimulatory pathways of B and T cell activation. The goals of these investigators are 1) to determine the mechanisms by which CTLA4Ig and anti-CD40L therapy inhibit the development and regulation of pathogenic B cells that secrete the autoantibodies responsible for tissue damage in SLE and 2) to identify the mechanism responsible for the powerful synergy between these two agents. In Specific Aims I and II the applicant will determine whether the regulatory effects of anti-CD40L and CTLA4Ig are mediated via naive hyper-reactive germ line encoded B cells that develop outside the germinal centers, somatically mutated and class switched B cells that arise within the germinal centers, and/or plasma cells within the long lived bone marrow compartment. They will do this by analyzing monoclonal anti-DNA antibodies generated from treated B/WF1 mice, and studying the expression of a particular autoreactive antibody gene that is highly restricted to anti-DNA antibodies in these mice. Subpopulations of autoreactive B cells bearing the R4A Tg anti-DNA HC will also be examined. T and B cell co-cultures will be used to determine whether the effects of these agents on B cells are mediated by modulation of the T cell compartment or whether B cell nonresponsiveness has been induced. Finally it will be determined whether these agents alter B cell responses to an exogenous antigen. The experimental tools the applicants developed will allow an examination of central and peripheral regulation of autoreactive B cells. These findings should help determine optimal regimens for delivery of CTLA4Ig and anti-CD40L to humans and help predict their safety profiles in the autoimmune host.